Hitherto, whole blood transfusion in which all the components of blood obtained by blood donation are subjected to transfusion has been the mainstream of blood transfusion. Attendant on the recent progress of technologies, however, blood component transfusion has come to be conducted in which the obtained blood is divided into blood components, such as red blood cells, platelets and plasma, and only the blood component needed by a patient is subjected to transfusion. With blood component transfusion, it is possible to alleviate the burden on the patient's circulatory system and other side effects, and effective utilization of the donated blood is promised.
When subjected to centrifugation, the donated blood is divided into a light supernatant PRP fraction, a heavy sedimentary CRC fraction, and a buffy coat (BC) formed therebetween. The buffy coat contains white blood cells, platelets and red blood cells, and in particular, the platelets include young active platelets in high proportion.
On the other hand, the buffy coat contains white blood cells and therefore cannot be utilized as is. In view of this, it is a common practice to extract only the buffy coat from the centrifuged blood, to subject it again to centrifugation so as to separate the buffy coat into a supernatant liquid and a sedimentary liquid, and further to remove white blood cells from a supernatant liquid by a white blood cell removing filter (see, for example, Patent Document 1).